CHAPTER 11: PROPERTIES OF LIQUIDS
Chem
1212
Dr. Aimée Tomlinson
Section 11.1
Solutions
What is a solution?
Solutions are formed from the addition of two species
Solute: dilute species
Solvent: abundant species
+
www.webmd.com/diet/slideshow-salt-shockers
Solution
=
thegldc.com/blog/tag/water/
gusville.com/index/LIS753/images/
Section 11.2
Energy Changes &
Solution Processes
Universal Solution Rule
Like dissolves Like
Polar/ionic species require polar solvent
Nonpolar compounds require nonpolar solvents
Energy Steps in Solution Formation
Step 1: solute is separated into its individual components – endothernic, ΔH1
Step 2: IF between solvent molecules are broken – endothermic, ΔH2
Step 3: IF are generated between solute and solvent – exothermic, -ΔH3
 H solution   H 1   H 2   H 3
On the left we have ΔHsolution < 0
Solute is completely soluble
E.g. NaCl in water
On the right we have ΔHsolution > 0
Solute is only partially soluble
E.g. CaSO4 in water
Section 11.3
Units of Concentration
Measuring Solute to Solvent
Mass Percent/Percent by weight
Molarity
M 
m oles of solute
L of solvent
 m ass of solute
M ass percent  
 m ass of solution
Parts per Million, ppm
Mole Fraction
A 
nA
n A  nB

nA
n tot
Molality
m 
m oles of solute
kg of solvent

  100%

ppm 
m g of solute
kg of solvent
or
g of solute
g of solvent
 10
6
Section 11.4
Factors that Affect
Solubility
Chemical Structure
Miscibility
How well two substances mix together
www.bridalwave.tv/alternative_hen/
Immiscibility
When two substances do not mix together
novocreamseparators.com/blog/clean-separation/
Partial Miscibility
Hydrophilic component will mix in water while hydrophobic part won’t
The longer he hydrophobic chain the less miscible it will be in water
Which one is more soluble in H2O?
CHCl3
CCl4
C6H11OH
CH3OH
NaF
MgO
Pressure
Primarily important for gases dissolved in solvent
Henry’s Law: gas solubility is directly proportional to gas pressure
Mathematically: Cgas = kHPgas
where Cgas is concentration of the gas in solution
kH is Henry's constant for this gas in a particular solution
As we increase the pressure we increase the number of gaseous moles we
can push into solution
The opposite is also true, reduce P we reduce concentration
Example Calculation
Calculate the solubility of oxygen in water at 20C and an atmospheric
pressure of 0.35 atm. The mole fraction of O2 in the air is 0.209 and
kO2 = 1.3 x 10-3 mol/L*atm. (Answer: 9.5 x 10-5 M)
Temperature
we have already mentioned that we can increase T to force
mixing between compounds
I should point out that if we are trying to mix polar and nonpolar
species no amount of heat increase will ever cause miscibility
previously, I eluded to the idea that the sign ΔHsoln of is a predictor
as to the solubility of two species
whille it is true to some extent there are many other factor which must
also be considered
to be technically correct we must perform experiments to truly
determine the extent of miscibility or immiscibility of two species
Section 11.5
Physical Behavior of Solutions:
Colligative Properties
Here they are …
Vapor Pressure/
Boiling Point Elevation
http://cirellio.files.wordpress.com/2008/06/boiling-water.jpg
Freezing Point
Depression
www.blog.thesietch.org/.../
Osmotic Pressure
Section 11.6
Vapor Pressures of
Solutions
Vapor Pressure & Temperature
VP increases as T increases
When T increases so do the
molecular motions & kinetic E
eventually allowing molecules to
escape from l to g
RULE: to go from l → g, VP must equal
atmospheric P
At higher elevations there is less
atmospheric P so less heat is needed
to boil (why water will boil below
100⁰C in Denver
Experiment – DI water vs Seawater
Over time, DI water is reduced as seawater increases
Water escapes from DI beaker faster
DI water liquifies back into the salt water beaker
The driving force is water wants to solvate salt
Recall ion-dipole forces are stronger (more stable) than Hbonding
This is why we use desicator packets to protect leather goods
TAKEHOME MESSAGE
The presence of a nonvolatile solute
lowers the VP of a solvent
Calculating Vapor Pressure
We use Raoult’s Law: Psolution   solvent  Psolvent
Example problem: What is the vapor pressure of water in a 50:50 mixture
of glycerol (DC3H8O3 = 1.261 g/mL) and water at 25C (PH2O = 23.8 torr)?
(Answer: Psoln = 19.1 torr)
Vapor Pressure for Volatile Mixtures
Petroleum Industry
Oil is composed of a number of different hydrocarbons
These all have similar but different boiling points
They can be separated through fractional distillation (see Section 11.10)
Raoult’s Law for a Volatile Mixture:
All ideal solutions obey this Law
Psolution 

i
 Pi
i
Example for Ideal Solution: Octane & Heptane
They possess the following similarities:
Size
Boiling point
Intermolecular forces (solute-solute,
solvent-solvent, and solute-solvent
Deviations from Raoult’s Law
Negative deviations:
Solute-solvent interactions are
stronger than solute-solute or
solvent-solvent one
Positive deviations:
Solute-solvent interactions are
weaker than solute-solute or
solvent-solvent one
Example of Volatile Mixture
At 20C, the VP of ethanol is 45 torr and the VP. of methanol is 92 torr.
What is the VP at 20C of a solution prepared by mixing 75g of
methanol and 25g of ethanol? (Answer: Psoln = 83 torr)
Section 11.7
Boiling Pt Elevation &
Freezing Pt Depression of
Solutions
Reminder: VP & Bpt Relationship
At boiling VP = Patm
Recall Seawater Experiment
The salt lowered VP of water
This makes a larger energy gap to
reach Patm
A larger gap means more heat
required to boil
TAKEHOME MESSAGE II
The presence of a nonvolatile solute
raises the boiling point of a solution
Boiling Point Elevation
Boiling point line is shifted when nonvolatile solute is added
Mathematically:  Tb  K b m solute
where ΔTb is the change in boiling point, Kb is a constant, and
msolute is the molality of the solute in solution
Example Bpt Elevation Problem
If the boiling point of a sample is 2.3 Celcius above the boiling point of
pure water, what is the molality of NaCl in the sample? K b , w ater  0.52 o C  kg / m ol
(Answer: 4.4 m NaCl)
Freezing Point Depression
Similar to Boiling Point
Salt melts ice by lowering the VP
This makes the freezing point lower
Lowering freezing point ends up
allowing water to melt above its
normal freezing point T
www.uniongas.com/images/meltingIcetechnology.jpg
Mathematically:  T f  K f m solute
Section 11.8
Osmosis &
Osmotic Pressure
Osmosis
When solvent passes through a
semipermeable
membrane
to
balance the solute concentrations
on each side of the membrane
Osmotic Pressure
amount of pressure needed to stop the solvent from flowing to the
more concentrated side of a semipermeable membrane
http://nanotech.sc.mahidol.ac.th/genchem/liquid1/osmo.jpg
  M RT
R  0.0821 mL ol atm
K
M  m olarity
T in K
Easy Example Problem
Calculate the osmotic pressure across a semipermeable membrane
separating seawater (1.14 M) from a solution of normal saline (0.31 M)
at a T = 20C. (Answer: 20 atm)
Difficult Example Problem
A solution was made by dissolving 5.00 mg of hemoglobin in water to
give a final volume of 1.00 mL. The osmotic pressure of this solution
was 1.91 x 10-3 atm at 25 oC. Calculate the molar mass of
hemoglobin. (Answer: 6.41 x 104 g/mol)
Reverse Osmosis
solvent is pumped through semi-impermeable membrane at a
pressure greater than  leaving behind solute particles
Used to purify water
www.goodhousekeeping.com/cm/goodhousekeeping/...
Section 11.9 & 11.10
Applications &
Fractional Distillation
Fractional Distillation
Mixtures are separated by this
method
Lower bpt components boil first &
collected at the top (e.g. petrol)
Higher bpt special boil last and are
collected at the bottom (e.g. crude
oil)
http://gcsesciencealive.co.uk/images/Fractional%20distillation.gif
Section
Electrolytic Solutions
Reminder: What are Electrolytes?
They are solutions possessing ions
They allow water to conduct electricity
Strong electrolytes dissolve completely (e.g. NaCl)
Weak electrolytes only partially dissolve (e.g. CaSO4)
Non-electrolytes do not dissolve inwater at all and are not ionic (e.g.
glycerol)
van’t Hoff Factor, i
Used to indicated the strength of the electrolyte
i
m oles of particles in solution
m oles of solute dissolved
What is i for the following?
LiF
What is i for the following?
MgO
What is i for the following?
Calcium Phosphate
True Colligative Equations
Electrolytes DO matter!!!
Example Problem
The van't Hoff factor for a 0.05 m solution of magnesium sulfate is 1.3.
What is the freezing point of the solution? K
 1.86 C  kg / m ol
(Answer: ΔTf = -0.12⁰C)
o
f, w ater
Bpt Example with i
If the boiling point of a sample is 2.3 Celcius above the boiling point of
pure water, what is the molality of NaCl in the sample? (Answer: 2.2 m
NaCl)
Conceptual Problem
For the list of compounds below rank them in order of increasing boiling
point, freezing point, osmotic pressure and vapor pressure. Assume a
1.0M solution for each reagent and complete dissociation where
applicable. C11H22O11, KBr, Li2SO4
First, we determine i for each compound.
C11H22O11 → i = 1
KBr → i =2
Li2SO4→ i = 3
Conceptual Problem
For the list of compounds below rank them in order of increasing boiling
point, freezing point, osmotic pressure and vapor pressure. Assume a
1.0M solution for each reagent and complete dissociation where
applicable. C11H22O11, KBr, Li2SO4
We use i,C11H22O11(i = 1), KBr(i =2), Li2SO4( i = 3),
and the mathematical equation for each trend
Boiling Point Trend:
 Tb  iK b m solute
C11H22O11 < KBr < Li2SO4
Conceptual Problem
For the list of compounds below rank them in order of increasing boiling
point, freezing point, osmotic pressure and vapor pressure. Assume a
1.0M solution for each reagent and complete dissociation where
applicable. C11H22O11, KBr, Li2SO4
We use i,C11H22O11(i = 1), KBr(i =2), Li2SO4( i = 3),
and the mathematical equation for each trend
Freezing Point Trend:
 T f  iK f m solute
Li2SO4 < KBr < C11H22O11
Conceptual Problem
For the list of compounds below rank them in order of increasing boiling
point, freezing point, osmotic pressure and vapor pressure. Assume a
1.0M solution for each reagent and complete dissociation where
applicable. C11H22O11, KBr, Li2SO4
We use i,C11H22O11(i = 1), KBr(i =2), Li2SO4( i = 3),
and the mathematical equation for each trend
Osmotic Pressure Trend:
  iM R T
C11H22O11 < KBr < Li2SO4
Conceptual Problem
For the list of compounds below rank them in order of increasing boiling
point, freezing point, osmotic pressure and vapor pressure. Assume a
1.0M solution for each reagent and complete dissociation where
applicable. C11H22O11, KBr, Li2SO4
We use i,C11H22O11(i = 1), KBr(i =2), Li2SO4( i = 3),
and the mathematical equation for each trend
Vapor Pressure Trend:
Pso ln   solvent Psolvent
 solvent 
n solvent
i  n solute  n solvent
Li2SO4 < KBr < C11H22O11
Example VP Problem with i
What is the VP of a solution containing 1L of water and 500 g of NaCl?
(at 25⁰C the VP of water is 23.8 torr) (Answer: 18.2 torr)